1. Field of the Invention
The present invention relates to a memory device and a memory access method which use a one time programmable (OTP) memory as a multi time programmable (MTP) memory spuriously.
2. Description of the Related Art
Memory devices that include, among other components, a frequency control OTP memory, a pseudo-MTP memory where a luminance control OTP memory is used spuriously as an MTP memory, and control circuits for controlling the frequency control and luminance control memories separately have been utilized as a memory device that stores information for controlling a display. Many integrated circuits that need a non-volatile memory employ an OTP memory in place of an erasable programmable ROM (EEPROM) to cut the process cost. OTP memories allow write operation only once. Pseudo-MTP memories are structured to increase the seeming number of times of rewrite by using a plurality of OTP memories. The use of these memories is popular. OTP memories and pseudo-MTP memories are known technologies and described in, for example, JP 2006-323981 A and U.S. Pat. No. 6,728,137.
In conventional memory devices that are provided in an integrated circuit for controlling a display device, the frequency control memory including an OTP memory and the luminance control memory including a pseudo-MTP memory are indispensable as well as the control circuits for controlling the frequency control and luminance control memories separately. The conventional memory devices therefore consume much power (current), take up a large area on the integrated circuit board, and are large in number of signal lines connected to peripheral circuits of the memory device, thus raising the cost of the integrated circuit. Another problem is that the frequency control OTP memory and the pseudo-MTP memory for adjusting the luminance differ from each other in operation and control method, which makes it difficult to give a memory device a single-memory structure. The pseudo-MTP memory which allows rewrite a plurality of times operates to read/write all memories sequentially, unlike the OTP memory where data is written only once and cannot be rewritten. The pseudo-MTP memory thus completely differs from the OTP memory in function, operation, and control method, and integrating the two different memories into one is difficult.
In integrated circuits that require a non-volatile memory, an OTP memory and a pseudo-MTP memory are originally used for different purposes and controlled by different control methods. However, most of peripheral circuits of the OTP memory and the pseudo-MTP memory are the same circuits. Nevertheless, making one of the OTP memory and the pseudo-MTP memory also serve as the other has not been practiced. Providing separate OTP memory and pseudo-MTP memory in the integrated circuit also means that the OTP memory and the pseudo-MTP memory have to be controlled individually, which takes up a large circuit area and makes the downsizing of the integrated circuit difficult.